Pyrolysis of alkylene glycol monoacyl esters



?atented Feb. 4, 1947 PYROLYSIS OF ALKYLENE GLYCQL MONOACYL ESTERS Thomas H. Vaughn, Grosse Ile, Mich, assignor to Wyandotte Chemicals Corporation, Wyandotte, Mich, a corporation of Michigan No Drawing. Application August 10, 194 i,-v Serial No. 548,941

1 Claim. 1

The present invention relates broadly to the manufacture of carboxylic acid esters of olefine alcohols, and more particularly to the manufacture of allyl acetate and allyl alcohol. The broad principle of this invention is based upon the pyrolysis of aliphatic, monoacylated ester of an alkylene glycol, yielding an organic ester of an olefine alcohol and other products.

It has been proposed to pyrolyze carboxylic acid diesters of alkylene glycols. This reaction gives rise to free carboxylic acid as well as the ester of an unsaturated alcohol.

It is an object of my invention to pyrolyze the monoacyl ester of those alkylene glycols. It is an object of my invention to pyrolyze the monoacyl esters of ethylene glycol and the monoacyl esters of other alkylene glycols which contain three or more carbon atoms in the alcohol nucleus. The former yield (among other products) vinyl esters and the latter yield allyl or substituted allyl alcohol acyl esters (among other products) when the non-substituted hydrocarbon group is respectively employed. The aforesaid reactions are thought to be represented by the following equations: 1 l

It is probable that the presence of isomeric forms of the alkylene glycols in such monoacyl esters is responsible for the various accompanying products formed in the pyrolysis. case of propylene glycol monoacetate such forms In the and their pyrolysis products are represented by the following formulae:

A. OHaGHOH-CH2OA0. (1 propylcylyimlmxmacetate) u t \l CHaCH=OHO.Ac CH2=CH.CH2OAO OHsCHzCHO B Methyltvinyl Allyl acetate Propionaldehyde ace a e B. CHaCHOAaCHzOH (2 propylene glycol monoacetate) (o I r z s. (c) CHFOEOHzOH (b) CH3CH=CHOH CH3OOAc=CH Allyl alcohol Propionaldchyde 0: Methyl vinyl acetate In addition, those of the above pyrolysis products which are esters, can in turn be hydrolyzed toform the following products:

(1) CH3CH2CHO (propionaldehyde) (2; CHz=CH.CHzOH (allyl alcohol) (3 CHs-C-CHs (acetone) certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed. It will be understood that other monoesters of these alkylene glycols, such as the monoacetate, monopropionate and the monobutyrate of propylene glycol, and the monopropionate and the monohexoate of ethylene glycol may be pyrolyzed and hydrolyzed. Aromatic acids can be employed, but these are not preferred.

The pyrolytic conversion of the propylene glycol monoacetate occurs in a temperature range of 250-700" C. This range is likewise applicable for the pyrolysis of other acyl esters of the glycols. With a catalyst a temperature of 600 C. or lower can be used.

A continuous method of operation employing a heated tube is usually employed for the pyrolysis. The yield of acetate is dependent upon the rate of feed of the vaporized propylene glycol monoacetate through the pyrolysis tube, the temperature and the nature of the increased surface area present in the tube and other factors. The same holds true for other acyl esters of olefine alcohols, wherein the reactant is an ester of either a different glycol or a different carboxylic acid or both. The pyrolysis will proceed satisfactorily in an unpacked tube, but packed tubes containing Raschig rings, glasswool, glass chips, porous plates, calcium chloride, granular charcoal, and the like, have the efiect of increasing the per cent of conversion for any given rate of flow or contact time. There are by-products formed in addition to water and unreacted propylene glycol monoacetate and these must be removed when pure or substantially pure allyl acetate is desired. 5

The following example serves to illustrate the invention, and more readily toenable the reader to understand and practice the same. While the hydrolysis is not a part ofsaid invention, it is included in the example, as it furnishes added proof of the components in the pyrolyzate.

Example The preheated vapors were led into a stainless steelpyrolysis tube, approximately 32" long by 1" outside diameter, likewise packed with glass I cohol and water.

4 Raschig rings and maintained at 525 C. by two electric heaters controlled automatically. The temperature was measured by means of thermocouples placed eight inches in from each end of said pyrolysis tube.

The vapors from the pyrolysis operation were condensed. The condensate was subjected to fractional distillation. The out up to C. contained water and allyl acetate, and its isomer methyl vinyl acetate some allyl alcohol and aldehydes. The cut in the range 110-120 C. contained primarily acetic acid, that at -19l C. contained unreacted glycol monoacetate and a little diacetate which can be reworked in the next run.

The aforesaid lowest boiling fraction after the addition of 1.8 times as much Water by weight was thereupon hydrolyzed using 5% sulfuric acid based upon the weight of the added water. This operation hydrolyzed l-acetoxy-l-propene (5 methyl vinyl acetate) into propionaldehyde and a part of the allyl acetate to allyl alcohol.

The propionaldehyde was distilled off between 48-52? C.; the acid catalyst was then neutralized with sodium hydroxide and a fraction containing allyl alcohol, unhydrolyzed allyl acetate and water taken off, leaving a residue. This mixed fraction was hydrolyzed by refluxing, using a 5% excess of sodium hydroxide beyond the phenolphthalein end point. This mixture was fractionally distilled to remove an azeotrope of allyl al- The allyl alcohol-water mixture was then dehydrated by adding benzene and distilling.

Other modes of applying the principle of my inventionmay be employed, changes being made as regards to'the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

e e o aim The process of pyrolyzing propylene glycol monoacetate which comprises heating it to a temperature of 425-525? C. thereby forming allyl acetate and isomers thereof, allyl alcohol, propionaldehyde and water, separating the fraction boiling below 110 (J. from the balance of thematerials subjected to such pyrolysis, and then deriving allyl alcohol from such fraction. 1

. TBQMA I UGHN- REFERENCES CITED UNITED STATES PATENTS Name Date h W d -1.-.-.-.-."r-'. A1 5: 1941 Number 

